Append two matrices in R without losing dimnames

Question

How can I append two matrices without losing the dimnames?

Set up some data:

m1 <- structure(c(35.3, 31.7, 25.9, 15.8), 
    .Dim = c(2L, 2L), 
    .Dimnames = structure(list(
     Treatment = c("no1", "yes1"), Loc = c("North", "South")),
    .Names = c("Treatment", "Loc")))
m2 <- structure(c(9.5, 9.6, 7.4, 4.0), 
    .Dim = c(2L, 2L), 
    .Dimnames = structure(list(
    Treatment = c("no2", "yes2"), Loc = c("North", "South")), 
    .Names = c("Treatment", "Loc")))

Which gives:

> m1
         Loc
Treatment North South
     no1   35.3  25.9
     yes1  31.7  15.8
> m2
         Loc
Treatment North South
     no2    9.5   7.4
     yes2   9.6   4.0

But if I append them with rbind:

> rbind(m1,m2)
     North South
no1   35.3  25.9
yes1  31.7  15.8
no2    9.5   7.4
yes2   9.6   4.0

I've lost the "Treatment" and "Loc" names on the row and column dimensions.

Is there a straightforward way to append the two without losing the dimnames?

It's okay in this case to either assume the dimnames are the same, or to assume we simply want whatever dimnames the first object has.

Answer 1

Here's one way:

out <- rbind(m1,m2)
names(dimnames(out)) <- names(dimnames(m1))

#         Loc
#Treatment North South
#     no1   35.3  25.9
#     yes1  31.7  15.8
#     no2    9.5   7.4
#     yes2   9.6   4.0